To identify organizations that have donated to the nonprofit in some year prior to the current year but have not contributed in the current year, the NPSP SYBUNT (Some Year But Unfortunately Not This year) report can be customized. Here's how to do it:
Navigate to the NPSP SYBUNT Report:
Go to the Reports tab.
Find and open the NPSP SYBUNT report template.
Customize the Date Range:
Click on the "Filters" pane.
Adjust the date range filters to include donations from the desired prior years and exclude the current year.
Modify Report Criteria:
Ensure the report is filtering by Account to get the organization-level data.
Add additional filters if necessary to refine the report (e.g., specific campaign or donation types).
Run the Report:
Save and run the report to get a list of organizations that have donated in previous years but not in the current year.
By customizing the date range on the NPSP SYBUNT report for Accounts, you can easily identify and target these lapsed donors for re-engagement campaigns.
Reference:
"Using NPSP Reports" from Salesforce Help: NPSP Reports
"SYBUNT and LYBUNT Reports in NPSP" from Salesforce.org: SYBUNT and LYBUNT

Before implementing the Accounting Subledger, review the following configurations:
Review Accounting Triggers:
Ensure that your Salesforce instance has the necessary triggers enabled to support the Accounting Subledger.
Go to Setup -> Triggers, and verify the status of triggers related to accounting functionalities.
Check Recurring Donations:
Navigate to NPSP Settings -> Recurring Donations.
Verify that the configuration aligns with the needs of the Accounting Subledger, ensuring proper allocation and tracking of recurring donations.
Payment Allocations:
Check the settings for payment allocations to ensure they are correctly mapped to the general ledger accounts used in your accounting system.
NPSP Settings:
Verify the overall NPSP settings to ensure there are no conflicts with the Accounting Subledger functionalities.
Reference:
Salesforce Accounting Subledger Documentation
Salesforce Nonprofit Success Pack (NPSP) Configuration Guide
Salesforce Trailhead: Configure Nonprofit Success Pack

https://powerofus.force.com/s/article/NPSP-Configure-Gift-Entry